A blind rivet has an outer, normally tubular body formed with an enlarged head at the "head" end and provided internally with a mandrel passing through the body having an enlarged head at the "tail" end of the body and a thin cylindrical stem protruding beyond the tail end of the body. In use, the rivet is typically placed in the riveting head of a power riveter and directed to the workpiece. In other instances, the rivet is placed in the workpiece and the tool then applied to it. The mandrel is gripped by a chuck of the riveting head, which is then operated to pull the chuck away from a fixed tip of the riveting head, thereby pulling the head of the mandrel against the tail end of the body to deform the tail end of the rivet body thereby forming a blind head. The rivet is constructed so that the mandrel stem breaks off inside the body when a predetermined load limit corresponding to a predetermined deformation of the rivet is reached. Similarly, the rivet may be set by the automatic riveter by rotating the mandrel, thereby breaking off the mandrel upon reaching a predetermined rotational stress limit.
In either event, the broken stem is allowed to exit rearward through a passage in the riveting head. In the case of a riveter which pulls the mandrel to separate the stem, the stem is abruptly pulled and released, expelling it from the riveting head through the passage In the typical power riveter of this type, the riveting head is actuated by a head piston The head piston may have attached thereto a rearwardly extending piston rod, or it may reciprocate on a stationary expulsion tube. The passage through which the stem exits the riveting head is directed through the piston and either the reciprocating piston rod or the stationary central expulsion tube.
In a power riveter of the pulling type, the stem can be expelled from the rear end of the riveting head with such force that it could penetrate soft tissue upon impact Even a stem which merely falls from the riveting head could strike the eye of a worker who is riveting overhead, potentially causing serious injury. Thus, it is known to augment the rear of the riveting head with a deflector for deflecting the stem away from the worker and down toward the riveter base. The drawback of using such a deflector is that the stems merely fall from the tool to the floor so that they must be cleaned up. Moreover, stems falling into the workpiece may damage the workpiece and stems falling onto the floor pose a danger to the operator or anyone else walking in the area. Accordingly, it is recognized that broken-off rivet mandrel stems should be collected and disposed of so as to avoid such hazards.
The most rudimentary means of avoiding the dangers of falling mandrel stems is to place a collecting bag over the end of the riveting head. Although such bags avoid the problems of falling stems, they engender problems of their own. Collecting the stems in close proximity to the riveting head allows the stems to fall back into the passage leading from the riveting head. Thus, stems tend to stack up and jam the passage through the head piston and piston rod. This malfunction can lead to costly downtime for unjamming and other repair.
An improved collection "bag" is disclosed in U.S. Pat. No. 4,137,747. The '747 collection device consists of a pair of concentric cylinders attached to the rear end of the riveting head. The cylinders have closed rear ends and normally nonaligned apertures and the outer cylinder is rotatable around the inner cylinder so that the apertures may be aligned, thereby allowing the collected stems to be discharged. The '747 collection device suffers from the same drawback as collection bags, that the stems tend to stack up and clog in the riveting head, although to a lesser extent. Another drawback is that the aperture is smaller than the cross-sectional area of collected stems, the result of which is that the operator must shake the riveter violently to discharge the stems out the aligned apertures because they are jammed together. One advantage over the collector bag is that the '747 device is taught as being made of clear plastic so that the operator can determine when the device is full of stems before the riveter stops working due to clogging. On the other hand, because non-opaque polymeric materials do not at this time have the scratch resistance to withstand the abuse directed to industrial tools, this benefit is of little lasting value.
It is known in the art to augment power riveters with a vacuum mandrel stem collection device for drawing the stems out of the riveting head and collecting them in a location either remote from the riveting head, as shown in U.S. Pat. Nos. 4,275,582 and 4,275,583, or adjacent to the riveting head as shown in U.S. Pat. No. 4,281,531.
The prior art recognized disadvantages in collecting mandrels at a location remote from the riveting head. Most importantly, such a scheme necessitated use of an additional hose from the power riveter to the remote collection site. The additional hose enhances the possibility of the worker entangling the riveter hoses with the workpiece or other objects, an inconvenient and potentially dangerous situation. Further, the additional hose may limit the reach of the device, the freedom of movement of the device and its access into confined areas or workpieces. Accordingly, the art has striven to locate the stem collection device adjacent the rear end of the riveting head. This location provides an additional important benefit. The stem striking the inside of the collector upon being expelled from the riveting head makes an audible noise. The worker using the power riveter uses this audible noise as an indication that the rivet stem has cleared the rivet head, freeing the rivet head for insertion of a new rivet. Accordingly, the worker uses the sound of the stem hitting the collection device to indicate when to remove the power riveter from the workpiece and place another rivet in the tip or on the workpiece, starting a new rivet cycle.
The most common rivet stem collection arrangement is shown in U.S. Pat. No. 4,281,531. This device has a storage canister located behind and directly adjacent to the riveting head. The canister has an end cap with a jet pump. A separate air line from the compressed air source is directed to the end cap and the pressurized air is directed through the passage in the end cap and expelled to the outside, thereby creating a vacuum in the storage canister which acts to suck the stem from the riveting head into the storage compartment. This design has multiple drawbacks. First, the removable end cap poses a safety hazard. If the power riveter is operated with the end cap removed, the falling or projected rivet stem may strike and injure the operator. Second, such systems collect in their jet pump orifices debris which has been carried by the vacuum along with the stems. Accordingly, such devices must be provided with a filter in order to prevent the jet pump from clogging. These filters are expensive to install and maintain.